The present invention relates to a noise reducing circuit for pixel signals and an image pickup device using this noise reducing circuit which, in the case where, as in a pixel output signal in a solid-state image pickup device, a signal component is multiplexed on a varying DC component, can cancel the DC component to derive the signal component accurately or can be less affected by an extraneous signal and, by doing so, can achieve a compact unit.
The CCD type solid-state image pickup device using a charge coupled device (CCD) and a CMOS type solid-state image pickup device have been known as a solid-state image pickup device for use in a video camera and electronic still camera.
For the CCD type solid-state image pickup device, a read-out signal is taken out as an amplified form through one amplifier provided in an output stage of a horizontal transfer section. Further, the amplifier can be constructed as a low input capacity on-chip amplifier. It is, therefore, possible to obtain a low-noise, high-quality video signal almost without involving a level variation for each pixel. Since, however, a signal charge sequentially transferred in the solid-state image pickup device is, as viewed as a signal current, very small on the order of 100 nA, it is susceptible to the extraneous noise and is adversely affected in its S/N ratio simply because the solid state image pickup device is located near a timing generator and digital signal processing circuit. It is, also, necessary to have a high mounting technique, as well as a proper arrangement of component parts, in the achievement of a compact camera. This, in addition to the ready susceptibility of the device to the extraneous noise, provides a bar to achieving a small-sized camera.
In the CMOS type solid-state image pickup device, on the other hand, amplifiers for deriving outputs of a respective plurality of photodiodes are incorporated, and a very weak signal current amplified thereby. The output of each amplifier is taken out as an image pickup signal through the scannings of corresponding vertical and horizontal scanning switches.
Since this kind of solid-state image pickup device uses a plurality of amplifiers for each pixel, if there occurs a variation, in a DC component, between the output voltages, then fixed-pattern noise is produced even at a light shutting time at an image pickup section.